Production of molded artificial masses



April 20, 1937. c. WULFF ET AL 2,077,542

PRODUCTION OF MOLDED ARTIFICIAL MASSES Original Filed Sept. 26. 1931 Cari H/ulff and Eugen Dorrer lNVENTORS ATTORNEYS Patented Apr. 20, 1937 UNITED STATES PATENT OFFICE PRODUCTION OF MOLDED ARTIFICIAL MASSES the-Main, Germany Original application September 26, 1931, Serial 565,286. Divided and this application March 26, 1935, Serial No. 13,066. In Germany October 2, 1930 9 Claims.

The present invention relates to'the production of molded artificial masses. This application has been divided out, from our copending application Ser. No. 565,286, filed-September 26th,

The polymerization of styrene, indene, vinyl acetate, acrylic acid and its esters or nitriles and like polymerizable mono-vinyl compounds, capable of forming resinous, thermoplasticpolymerization products, and of mixtures of the said mono-vinyl compounds can be carried out in a simple manner, as for example by heating with or without the employment of catalysts, such as organic peroxide, as for example benzoyl peroxide or peracetic acid or tin tetrachloride. The

polymerization products, however, are obtained as a block or in some other compact form according to the shape of the reaction vessel. In this form they can only be withdrawn from the reaction vessel with difficulty even' when hot and, moreover, in order that they may be employed for lacquers or for pressure molding or injection molding compositions, they must be in a com minuted form. The comminution is usually effected by mechanical methods, as for example by turning, planning or grinding. Ihis is expensive and offers difliculties in many cases, because the material becomes warm and consequently plastic during the comminution and sticks in thecomminuting apparatus or tool. Besides this, the products resulting from the polymerization in the hitherto usual manner do not show a very high mechanical strength and are not uniform, which disadvantages impair the usefulness of the polymerization products for many purposes. It has been also suggested to allow the initial material to be polymerized to flow through an inclined heated pipe so that it is'subjected to the temperatures considered necessary for the polymerization for rather a short time only. For the same purpose and for avoiding discoloration, solutions of the initial materials have been forced through the said pipes or similar apparatus whereby solutions of the resinous polymerization products are obtained. In both cases, however, the products are not substantially improved in comparison to those prepared without the said precautions. Especially when working in the presence of solvents the drawback is that it is diflicult to completely remove the solvents from the polymerization product, if it be desired to obtain it in the solid state. This removal is either incompletely ataned or the solid products are'considerably impaired by strong distillation or by acting thereon with steam. Another method which has been suggested for the polymerization of vinyl esters consists in polymerizing the said bodies by heat and adding cold vinyl ester as soon as the polymerization has set in, incompletely polymerized ester in mixture with non-polymerized ester being continuously drawn off whereupon the mixture is completely polymerized under reflux. While explosions can be thus avoided, the products are not homogeneous.

We have now found that polymerization can be effected in a very convenient manner and moreover products having a hitherto unknown mechanical strength are obtained from monovinyl compounds, such as vinyl esters, as for example .vinyl acetate, vinyl chloroacetate or vinyl chloride or mixtures thereof, and especially from mono-vinyl aryl compounds, such as styrene, chlorostyrene (vinyl chlorbenzene) and vinyl naphthalene, by avoiding, in the complete heatpolymerization, any substantial autopolymerization of the viscous primary polymerization products obtained from the said mono-vinyl compounds. The term complete polymerization means that the whole material intended for polymerization is polymerized to a substance which is solid at normal temperatures. By avoiding the autopolymerization i. e. the polymerization catalyzed by the presence of polymerization product initially formed, and the considerable evolution of heat caused by said autopolymerization, solid products can be obtained which show a mechanical strength extraordinarily superior to that of the products obtainable by the hitherto known processes, especially in the case of the said vinyl aryl compounds.

We have found that the autopolymerization can be avoided by removing heat from the whole viscous mass of the batch'under treatment as soon as the temperature rises above that intended for polymerization at the most by 10 C. preferably not more than 5 C.

When the initial material is heated for some t me in the hitherto usual manner the whole mass becomes viscous, the degree of viscosity depending on the initial material, on the nature of the catalyst employed, if any, and on the temperature employed. On heating styrene, for example, to its boiling point, the increase in visc sity takes place rather rapidly and the temperature rises quickly considerably above the boiling point of styrene C. at normal pressure) in many cases up to C.

The development of heat and the deleterious eiiects resulting therefrom are avoided according to the present invention by "concentration cooling". An efllcient removal of heat from the highly viscous batch by external concentration cooling" is possible only when working on a very small scale, for example. in vessels having a reaction space of up to 1 liter or in narrow pipes having an internal diameter of at the most say 5 inches, but even in this case the internal temperature must be controlled which feature is diillcult to carry out in the said narrow pipes. We prefer therefore to work in large vessels which may be of any size, if they be provided with means for concentration cooling". By the term "concentration cooling we wish to define all kinds of cooling by which the concentration of the homogeneous viscous mass in polymerized product is maintained or even increased, that means any kind of cooling which is carried out in such a manner that the proportion of polymerized product in the said homogeneous mass remains the same or is increased. during the cooling (cooling methods according to which cold diluents capable of mixing with the homogeneous, viscous mass or non-polymerized cold initial materials are introduced into the said mass in such an amount that, by the introduction of the said diluents, the proportion of polymerized product in the resulting whole mass is smaller than that before the introduction of the said diluents being outside the scope of concentration cooling). For the sake of brevity the said specific method of cooling will be referred to in the following disclosure and in the appended claims as "concentration cooling".

The said method can be carried out in various ways. Thus for example volatile constituents can be evaporated from the batch, without returning them in the cold state, so that the evaporation withdraws heat from the mass. Since, however, the mass is usually not heated to its boiling point for reasons which will be explained later, we prefer to connect the reaction vessel to an evacuating device, such as a pump, so that the boiling point of the initial material is reduced and non-polymerized initial material may be evaporated as soon as a certain temperature is attained. This feature allows an exact control of the temperature within the mass. If it be desired to carry out the polymerization, for example of styrene, at 90 C., the initial batch oi monomeric styrene is slowly heated to say C. whereupon the pressure in the reaction vessel is reduced to 100 millimeters (mercury gauge) at which pressure styrene bolls at C. Should auto-polymerization set in on further warming and the temperature rise to say 90.5 C., monomeric styrene is sucked off with the absorption of heat by evaporation thereby cooling of the whole batch and giving a slight increase in the viscosity of the mass under treatment. It will be easily understood that this method works quite automatically. It can be applied of course only when polymerizing at a temperature below the boiling point of the initial material. As will be shown below this necessity is, however, valuable for several reasons.

Another method of concentration cooling consists in arranging within the reaction vessel suitable devices for indirectly cooling with a fluid i. e. with liquids or gases, such as nitrogen, carbon dioxide or air. Thus, for example, pipe coils may be arranged within the vessel, or straight pipes or other similar devices passing through the vessel or other small vessels may be arranged within the reaction vessel in the manner usu y ployed for internal cooling or heating. The vessel may be provided with the usual means for controlling temperature, such as thermometers or electrically recording thermo-elements, the liquid or gaseous cooling agent being passed through the cooling means as soon as the temperature within the batch rises above the polymerization temperature intended. The quantity of cooling agent employed depends of course on the nature of the reaction vessel and of the cooling devices arranged therein, the cooling effect being increased, if desired, by any usual and convenient method, for example, by providing the cooling pipes or vessels with ribs. Instead of controlling the flow of the cooling liquid or gas by hand or complicated automatic devices actuated by the temperature controlling devices, a liquid may be employed for cooling which has a boiling point corresponding to the temperature desired for the polymerization. For example water may be employed, if the polymerization is to be carried out at C. As soon as autopolymerlzation with rise of temperature sets in, the liquid passing through or contained in the cooling device is then at least partially evaporated, so that the cold of evaporation reduces the temperature of the polymerizing batch which is thus kept at 100 C. if water be employed. Instead of water methyl, ethyl, propyl or butyl alcohols, di-ethyl or propyl ethers, benzene, toluene, gasoline, mixtures of ethylene glycol and water or aqueous solutions of water-soluble salts may be employed so that the temperature may be kept constant at the diilerent temperatures corresponding to the boiling points of the said liquids at normal atmospheric pressure. The boiling points oi the liquids can of course be varied if they are kept in the cooling device under somewhat increased or reduced pressure.

In the process according to the present invention polymerization accelerators, such as oxygen or benzoyl peroxide, glacial acetic acid, acetic anhydride, peracetic acid or other organic peroxides, or completely or incompletely polymerized mono-vinyl compounds may be employed, which permit one to carry out the polymerization in a commercially reasonable period of time even at rather low temperatures. The said accelerators are generally employed in amounts of from 0.01 to l per cent of the initial material, these amounts varying somewhat with the specific initial material employed. In most cases from 0.05 to 0.5 per cent of the initial material is suillcient for obtaining an efllcient acceleration.

Very important features especially on working with styrene are the temperature of polymerization and the purity of the initial material.

By the polymerization at temperatures below the boiling point of the initial vinyl compounds the resistance of the solid products to bending by heating under a load (Martens' test) is not only substantially improved, but the resistance to mechanical influences is also increased. The solid products hitherto prepared from styrene have never reached a strength of 12 cm. kg./cm. in the V. D, E. impact test (for this and-Martens test compare Vorschriftenbuch des Verbandes Deutscher Elektrotechniker, 17th ed. of 1930, pages 196 and seq. and British Plastics and Moulded Products Trader, vol. 2, 1931, pages 558 and seq). On working in accordance with the present invention, however, solid products can be obtained which have a strength considerably above 12 cm. kg./cm. Thus, for example, solid polymerization products can be obtained from styrene which show the following values of strength and resistance to bending on heating under a load according to Martens.

l i in R t Polymerization m In Martens test temperature 2i? a stable at oentigrade 120 12 6) 68 98 CO 100 14 650 70 90 to 92 13 700 70 85 22. 5 750 78 70 lo 80 25 to 30 8m 80 Particularly high values in the Martens test are obtained, if the polymerization be carried out in partial vacuo.

Preferably, the highest polymerization temperature intended is not applied from the start, but the initial material, say styrene, is slowly heated first to say 50 C. and kept constant at this temperature for say 40 hours by concentration cooling; if 0.05 per cent, by weight of the styrene, of acetic anhydride is added, this period may be reduced to say 10 hours. The temperature of the batch is then slowly raised to 85 C. and kept constant at this temperature for hours, or if acetic anhydride be used for 12 hours, employing 30 concentration cooling by pumping water heated to about 80 C. through a pipe coil arranged in the reaction vessel, so that a temperature of 87 C. or higher does not occur anywhere in the reaction vessel. Similar precautions can be applied when working at other temperatures.

Generally, the polymerization is carried out at a temperature between 30 C. and the boiling point of the initial material and, in the case of styrene, preferably at from 95 degrees to 25 degrees C. below its boiling point. Very low temperatures, such as from 10 to 30 C. may be applied in the case of styrene, but in this case the polymerization requires an unduly long period of time even in the presence of a polymerization accelerator.

The purity of the initial material should be as high as possible, since in the case of styrene, for example, the presence of any substantial quantities, i. e. from about 2 to about 3 per cent of the styrene, of benzene, xylene or ethyl benzene, reduces the mechanical strength of the solid final products. If products elastic to bending be desired which become more plastic on heating, additions of softening agents, such as phthalic es- 55 ters, hydrocarbons of high boiling point, as for example benzyl naphthalene, tricresyl phosphate, chlorinated naphthalene, acrylic esters, India rubber and like softeners may be added. Fillers asfor example zinc oxide, quartz dust, lamp- 60 black, pigments, fish scale preparations or extracts or dyestuffs, either alone or in conjunction with softeners, added before or after the start of the polymerization, may be employed, but the amounts of these solid substances should not be higher than 50 per cent by weight of the styrene.

In the foregoing we have mainly described the polymerization of styrene, since the difliculties in obtaining valuable products from this vinyl aryl compound and its analogues, such as vinyl toluene, vinyl chlorbenzene or vinyl naphthalene, are much greater than in the case of aliphatic vinyl compounds, but the specific features of the process according to the present invention are also most valuable in the polymerization of aliphatic vinyl compounds, such as vinyl acetate or acrylic 'butyl ester or mixtures of both, or mixtures of these with styrene.

As explained in the introductory paragraphs it is often rather difiicult to comminute the solid polymerization products.

We have found that the polymerization products are obtained in a particularly simple manner in such a form that they may be readily pulverized, dissolved, comminuted or rolled out, if after the polymerization, the hot or further heated reaction product, while still soft or plastic, is pressed out from the reaction vessel by the action of a difference in pressure,which diiference may be produced by the utilization of increased internal or reduced external pressure. For example, by the use of suitably shaped nozzles, threads or sticks may be directly produced which, after leaving the nozzles, are still plastic for a certain time and may therefore readily be collected continuously, for example on spools or bobbins. By withdrawing the product in this manner there is obtained the further advantage that even small remainders of non-polymerized products are readily removed by evaporation. The temperatures necessary for rendering the polymeric styrene soft and plastic are generally above 120 C. the plasticity rising with an increase of temperature. For injection-molding temperatures of from about 160 to about 220 C. are usually employed. With other vinyl compounds the temperatures for softening vary depending on the initial material, polymeric aliphatic vinyl compounds, such as polymeric vinyl acetate, requiring lower temperatures than polymeric styrene, for example from about 120 to 150 C., for injection-molding. In the case of pressure-molding or producing powders for pressure casting or injection-molding our improved polymerization process is of special importance, because even small amounts of non-polymerized initial materials or of solvents lower the softening point considerably. If the outlet is a constructed as a nozzle, the reaction product may be pressure-cast or injection-molded" by directly pressing it into closed molds. By pressure-molding a process is meant in which a. batch of the material is placed into an open mold or matrix, and pressed therein into the desired shape by pressing with a suitable die, or patrix if desired while heating; on the other hand the material to be molded may be preheated or both steps may be taken. In pressure-casting, or injection-molding, a closed mold is employed with a narrow, usually funnel-shaped, inlet through which the fused or plasticized material is hydraulically or otherwise pressed into the mold so as to completely fill up all the cavities of the mold even if very intricate moldings are to be produced. In this latter method the material is preferably supplied to the pressing device in the form of a powder or of small grains, the powder or grains then being heated at least in the neighborhood of the nozzle so that a homogeneous more or less viscous liquid passes into the mold. Since the process of pressure-casting or injection-molding is well known in the production of small metal articles we need not give a detailed description of it here.

An apparatus for carrying out the continuous polymerization is shown in the drawing annexed hereto. In this apparatus we have embodied all of the provisions described abovebut we do not wish to be restricted to such combination, the several single features being applicable singly and without the combination described. In the drawing is shown in cross-section a cylindric vessel a which may have a height of from 2 to 8 meters and a diameter of from 0.3 to 2 meters respectively; the vessel may consist of chromium-nickel steel or aluminium or maybe lined with aluminium or may be enamelled. In the upper and lower portions of the vessel two separate pipe coils b and c are arranged. the coil b serving for initial heating and for concentration cooling and the coil c serving for fusing the polymerization product. If desired the number of the coils may be increased. a plurality of the difierent coils being advantageous when working in large vessels. The bottom of the vessel is shaped as a funnel and connected to an outlet pipe d. which ends in a slot or nozzle e and in which a worm conveyor 0 with a pulley h is arranged. The pipe (1 is partly or wholly surrounded by a heating coil I or any other suitable heating device. Below the slot or nozzle is arranged an endless conveyor belt m running on the rolls 1' and k.

The following examples will further illustrate how the present invention may be carried out in practice but the invention is not restricted to these examples.

Example 1 .Monomeric styrene is introduced into an internally enamelled kettle which contains an enamelled closely wound tube coil through which liquids for heating or cooling can be passed. By means of lubricating oil heated to C. and passed through the coil the styrene is slowly heated to 60 C. and kept at this temperature until it becomes viscous which result is obtained after about 40 hours. The oil passing through the coil is then warmed to C. and the viscous mass is thus warmed to the said temperature and kept constant thereat for about 25 hours, any heat developed by autopolymerization being drawn ofi by the oil the temperature of which is kept between 80 and 90 C. after the mass has been heated to 90 C. so that the temperature of the mass does not rise above C. The viscous mass is then successively slowly heated in the same manner to C.. and C. for 5 hours each. The finished polymerization product is then fused by heating to from to 220 C. and removed from the kettle. To this end, the kettle may be provided with an ascending pipe reaching to its bottom and capable of being heated. When the reaction is completed. the reaction product can be forced from the ascending pipe and discharged through a nozzle 1 millimeter in diameter by pressing nitrogen into the vessel at a pressure of 30 atmospheres and the reaction product leaves the nozzle in the form of a thread.

which may be comminuted very readily after solidification, or can be wound on a spool.

Emmple 2 Monomeric styrene. which contains 3 per cent by weight of ethyl benzene and to which 6 per cent of tricresyl phosphate have been added as a softening agent, is forced under a pressure of 30 atmospheres through a pipe oi about 5 meters length and 4 square centimeters cross-section. which is coiled in the form of a spiral and contains several thermo-elements. The coil is situated in a hot bath kept at a temperature of from 110 to 120 C. The outlet from the pipe is constructed in the form of a nozzle of about 1 millimeter in diameter below which a spool is arranged upon which the polymerization product issuing from the nozzle is continuously wound. By working in the said apparatus under the said conditionsiromstookilogramsofasolidpolymerization product having a strength of about 12 cm. kg./cm. in the V. D. E. impact test may be obtained in the course of 24 hours, the product being easily comminuted and then useful for iniection-molding.

Example 3 30 kilograms of monomeric styrene and 10 kilograms of solid polymeric styrene are polymerized by heating to about 95 C. in a vertical cylindrical vessel of aluminium having a content of about 200 liters and a lower heating coil arranged therein as shown in the drawing and through which water heated to 95 C. is passed. until a viscous mass is formed. After from 5 to 6 hours about 5 liters of styrene are then added per hour until the bottom of the upper coil is covered. The styrene in the lower portion of the vessel is then completely polymerized to a solid mass. 'lhis mass is then softened by heating the lower coil to from 180' to 220 C. with the aid of steam or oil while the polymerization of the styrene in the upper part of the vessel is carried out at 95 C. The finished polymerization product-is drawn of! at the bottom at the rate at which monomeric styrene is added at the top. The temperature of 95 C. is maintained owing to the bad heat-conductivity of the viscous polymerisation product. Through the funnel shaped bottom of the vessel which is connected with a pipe provided with heating means and a worm conveyor, the pipe being closed by a plate provided with a slot being narrowed to form a slot. the hot, plastic polymerization product is drawn oi! through the slot from which it is taken oil by an endless belt and can be easily disintegrated after cooling. The apparatus described is capable of producing polymerized styrene in a quantity of about twice the volume of the vessel per day. Instead of styrene. its homologues, such as methyl or di-methyl styrene, vinyl chlorbenzene, vinyl phenol, vinyl acetate and similar compounds can be polymerized and disintegrated in a simple manner. The hot plastic polymerization product may be directly pressed at about 200 C. into a closed mold by means of the worm conveyor or an additional injection machine so that molded articles are obtained by injection-molding. or the disintegrated cold material may be fed into an injection-molding machine in which it is heated to from 180 to 220 C. before entering into the mold. In this manner the most intricate molded articles, such as covers for electric switches or other electric insulating articles for electric or wireless apparatus of any kind. vanity boxes, powder boxes, knobs. handles, buttons, or transparent or colored artificial Jewelry may be obtained in a very simple and cheap manner.

Example 4 In a kettle provided with a refiux condenser and an outlet at the bottom. styrene is polymerized by heating to from 80 to 90 C. for 30 hours at a pressure of 100 millimeters of mercury.

Any monmeric styrene distilled oil. into the condenser is returned into the process or'em- .ployed in another operation. In testing rods of 60 millimeters of mercury a product is obtained which shows a strength in the impact test of 25 kilograms per square centimeter, a break load on bending of 800 kilograms per square centimeter 5 and a resistance in the Martens test to heating to more than 80 C. The products can be easily molded by injection-molding or by heat-pressure molding. If desired, the product may be removed from the reaction vessel by fusing at about 180 C. and introducing nitrogen at the top of the vessel at a pressure of about 10 atmospheres.

Example 5 In the interstice oi. a double-walled vessel,

styrene containing 0.05 per cent of its weight of benzoyl peroxide is heated for 24 hours to a temperature between 95 and 105 0., by heating water in the inner vessel to 98 C., the temperature being maintained by eventual evaporation of water in the inner vessel. After about 48 hours the styrene is polymerized to a. solid mass which has a strength in the V. D. E. impact test of 17 cm. kg./cm. and becomes plastic at from 180 to 220 C. After heating the product to 25 from 200 to 220 C. the product is removed from the vessel. If desired, a mixure 01. 70 parts of styrene with parts of acrylic butyl ester may be subjected to the polymerization described, the product having a strength of 20 cm. lag/cm 30 a resistance to bending of 500 kg./cm. and a resistance to heat of C.

If the polymerization is to be carried out at about C. benzene or ethyl alcohol is introduced into the inner vessel.

What we claim is:

1. The process of producing molded articles which comprises heat-plastifying at a temperature above about C. a polymeric mono-vinyl compound and injecting the plastifled material into a mold.

2. The process of producing molded articles which comprises heat-plastifying at a temperature above about 120 C. polymeric styrene and injecting it into a mold.

3. The process of producing molded articles which comprises heating polymeric styrene to from to 220 C. and injecting it into a mold.

4. Injection-molded articles comprising polymeric mono-vinyl compounds.

5. Injection-molded articles comprising polymeric styrene.

6. Injection-molded articles comprising a polymeric styrene which has an average strength of from 12 to 25 cm. kg./cm. in the impact test of the Verein Deutscher Elektrotechniker at a temperature of about 20 C.

7. Injection molded articles consisting of a p01 ymeric styrene which has an average strength of from 12 to 25 cm. kg./cm. in the impact test of the verein Deutscher Elektrotechniker" at a temperature of about 20 C.

8. Injection molded articles comprising polymeric acrylic acid esters.

9. Injection molded articles comprising polymeric vinyl chloride.

CARL WULFF. EUGEN DORRER. 

